1. Field of the Invention
The present invention relates to a tone control apparatus for executing a boost process on a predetermined band of a signal.
2. Description of the Related Art
Audio devices employ tone control apparatuses for executing a tone control process such as a boost process for increasing levels of predetermined frequency bands. In the boos process, as shown in FIGS. 7B and 7C, when an amplitude value of an audio signal is large, an audio signal in a boost band is in a clip state at a supply voltage, and thus an audio output from a speaker is distorted.
In order to solve this problem, applicants propose a tone control apparatus described in JP publication number 2010-109845. In this tone control apparatus, a first detecting section and a second detecting section detect a case where an output voltage of an amplifying section has a first set value or more and a case where the output voltage has less than a second set value. That is to say, a case where the output voltage of the amplifying section is clipped to a high-level side, and a case where the output voltage is clipped to a low-level side are detected. A synthesizing section synthesizes these detected results, and a switching section switches a boost amount of a boost processing section based on an output voltage of the synthesizing section. Therefore, when the output voltage of the amplifying section is clipped to the high-level side and clipped to the low-level side, the boost amount is switched into a second boost value smaller than a normal first boost value. For this reason, the output voltage of the amplifying section can be prevented from being clipped without reducing an amplitude of all bands.
In this tone control apparatus, however, even when the boost amount is switched into the second boost value, if a volume level is high, the output voltage of the amplifying section is occasionally clipped.